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    <script>
        /**
         * promise三种状态
         * pending fulfilled rejected
         */
        var p = new Promise((resolve,reject)=>{

        })
        var f = new Promise((resolve,reject)=>{
            resolve(10)
        })
        var r = new Promise((resolve,reject)=>{
            reject(20)
        })

        console.log(p);     //Promise {<pending>}
        console.log(f);     //Promise {<fulfilled>: 10}
        console.log(r);     //Promise {<rejected>: 20}
    </script>
</body>
</html>